A known pulse width modulated (PWM) inverter includes a center tapped power supply with positive and negative terminals, the center tap being connected to neutral or ground. The positive and negative terminals are connected to a low pass output filter through respective switches which may be transistors or the like. The inverter switches are controlled to alternately conduct current to the output filter, the switches providing a pulse width modulated waveform to the filter, which in response thereto, provides an AC output which is applied to a load.
One problem with such known PWM inverters is the ability of the DC power supply to cope with regenerative currents flowing from the load. Regenerative load currents may be quite large, a load on an aircraft, for example, typically having a power factor of 0.75 lagging to unity. In applications, such as on an aircraft, where the inverter load may be reactive, the power supply typically includes a pair of capacitors for accepting all of the regenerative load current, one capacitor being connected between the positive terminal and center tap of the power supply and the other capacitor being connected between the negative terminal and center tap of the power supply. One capacitor accepts all of the regenerative current flowing when one of the inverter switches is on, while the other capacitor accepts all of the regenerative current flowing when the other inverter switch is on. During the generation of each half-cycle of the AC output, one of the inverter switches is typically on a greater amount of time than the other switch resulting in an uneven distribution of charge on the power supply capacitors since one of the capacitors must accept more regenerative current than the other capacitor. Further, the power supply capacitors in such known PWM inverters typically cannot discharge while a regenerative current is flowing to the power supply so that each capacitor must store all of the regenerative current flowing thereto during the generation of each half-cycle. Since the regenerative current is not distributed evenly among the capacitors during the formation of each half-cycle of the AC output and because the capacitors cannot discharge while a regenerative current is flowing to the power supply, the power supply capacitors must be quite large.